A group headed by Dr.
Xiao Hu, a Principal Investigator in International Center for Materials Nanoarchitectonics (WPI-MANA; Director-General: Masakazu Aono), National Institute for Materials Science (President: Sukekatsu Ushioda) elucidated a new phenomenon that occurs in multi-band superconductivity. Multi-band superconductivity is a phenomenon in which electrons in different orbitals in compounds such as MgB
2 and iron pnictides enter superconducting state simultaneously, and is considered to be the key to realizing room-temperature superconductivity.
In this work, the research group focused on a superconductor having 3 components which are subject to mutual repulsive force caused by electron Coulomb interaction. Competition between the components produces a frustrated superconducting state characterized by mutual shift of the superconducting phases. As a result, the relative phase oscillation called Leggett mode becomes soft, resulting in a zero-energy collective excitation. It was shown theoretically that this phase-frustrated state exists stably without attenuating the amplitude of superconductivity. It was also found that experimental results for the low-temperature electronic specific heat of iron-based conductors can be explained satisfactorily by the zero-energy Leggett mode. As the Leggett mode is considered to be the only zero-energy collective excitation in superconductivity, its elucidation is important for understanding the essential nature of superconductivity. The phase frustrated superconducting state is also expected to have important applications such as new implementation of qubits and high-accuracy SQUID.
This research result was published in the scientific journal Physical Review Letters of the American Physical Society.
